1. Technical Field
The present disclosure relates to intravascular catheters used for treating a stenosis in various blood vessels and other bodily conduits with radiation to inhibit restenosis, e.g., after angioplasty or other cardiovascular procedures, and particularly to an intravascular catheter reinforced with at least one stiffening mandrel to improve the pushability and maneuverability of the catheter as it moves through the circulatory system.
2. Background of the Related Art
Various techniques have been developed to treat many different conduits in the body when these conduits have become reduced in size due to the existence of a stenosis or have been completely occluded. These techniques include introducing a deflated balloon catheter to the site of the stenosis or occlusion, inflating the balloon one or more times to reduce the size of the stenosis, deflating the balloon and then removing the balloon catheter from the treatment site.
With respect to the vascular pathways, angioplasty is routinely used to open an artery or blood vessel in the region where the stenosis or the occlusion has occurred. A typical angioplasty procedure consists of making a small incision through the body and into a blood vessel and then maneuvering a guidewire through the vascular system to a point beyond the stenosis or occlusion. A hollow catheter with a deflatable balloon near its distal end is threaded over the guidewire and advanced to the point of stenosis or occlusion. The balloon is then inflated and deflated several times to widen the constricted area, and is then withdrawn from the body.
Unfortunately, although the angioplasty procedure does markedly reduce the area of stenosis or occlusion, many patients exhibit a reoccurrence of the stenosis within a few months of the original procedure. Although the original stenosis occurs by means of the build up of plaque over a relatively long period of time, studies have led many to believe that the reoccurrence of the stenosis after the original angioplasty procedure is unrelated to the cause of the original stenosis. It is believed that the inflation of the balloon catheter used in the angioplasty procedure or the placement of a stent in the area of the stenosis causes irritation to the blood vessel. This irritation produces a mechanism of action called hyperplasia, inducing the inner layer of the blood vessel cells to rapidly reproduce, thereby causing restenosis. It has been discovered that if the blood vessel is irradiated at the point of the stenosis with a radioactive dose immediately following the angioplasty procedure, the mechanism that causes hyperplasia would be inhibited without harming the blood vessel itself.
Accordingly, following the angioplasty procedure, the guide wire is typically left within the patient and an intravascular catheter is introduced over the guide wire. The intravascular catheter is pushed and maneuvered through the circulatory system until a distal end of the catheter is in proximity to the site of the angioplasty procedure. A source wire having at least one radioactive dose at a distal end is then advanced through the interior of the intravascular catheter until the distal end reaches the site of the angioplasty procedure. The radioactive dose is then left inside the catheter for a specific period of time to treat the area of the original stenosis.
It is often difficult to maneuver the intravascular catheter within the circulatory system, especially within narrow blood vessels such as the coronary arteries. To aid in steering and maneuvering the intravascular catheter through the circulatory system, a need exists to stiffen at least a portion of the intravascular catheter for allowing the intravascular catheter to be maneuvered through the circulatory system without crimping.
Additionally, during the radiation procedure, it is important to precisely control the amount of radiation which is directed to the blood vessel wall, since too much radiation could cause tissue damage while too little radiation could fail to inhibit hyperplasia. Therefore, a further need exists for properly positioning the radioactive dose within the blood vessel to address these issues.
The present disclosure is directed to a catheter and a method for performing radiation treatment at a site where angioplasty was performed. The catheter includes a hollow, cylindrical member constructed from a fairly flexible material. The catheter is maneuvered within the body by traveling over a guidewire which was initially maneuvered in the blood vessel to a position beyond the actual site of a stenosis. The catheter is slightly tapered at its distal end to facilitate movement through blood vessels or similar conduits or ducts. Stand-off structure having a stand-off balloon surrounds a portion of the outer surface of the catheter.
The distal end of the catheter includes an inner lumen plug and a distal mandrel extending through the inner lumen plug. The distal mandrel is manufactured from shape memory alloy, such as a nickel-titanium alloy, to stiffen and reinforce the catheter when the catheter is introduced within the blood vessel. This adds strength to the distal end of the catheter which prevents the distal end of the catheter from crimping as the catheter is pushed and maneuvered through the circulatory system.
The stand-off balloon when inflated is preferably smaller in circumference than the circumference of the blood vessel, such that the inflated balloon is bumped-off from the inner surface of the blood vessel to provide some space between the inflated balloon and the blood vessel. This would allow blood to profuse through the space during the radiation treatment.
The method of the present disclosure entails that once the site of a stenosis is determined by appropriate diagnostic procedures and angioplasty is performed, the catheter with the stand-off balloon being deflated is threaded over the guidewire and is advanced such that the stand-off structure is maneuvered to the area where angioplasty was performed. The distal mandrel can also be used in conjunction with a longer fixed or removable stiffening mandrel for assisting in the maneuverability and positioning of the catheter within the circulatory system.
Once the stand-off balloon is verified to be in position, the stand-off balloon is inflated and kept inflated to bump-off the catheter from the walls of the vessel. One or more radioactive sources are provided on, or inside the distal end of a flexible source wire which is advanced through the interior of the cylindrical member of the catheter until it reaches the proper location. The radioactive source is then left inside the catheter for a specific period of time to treat the area of the original stenosis.